The arbitral decisions under Articles 21.3(c) of the DSU raise various legal questions that may poses a threat to the certainty and predictability of the WTO regime. This paper explores the potentially relevant factors for determining implementation periods, and performs a critical analysis of the difficulties arbitrators face when determining reasonable implementation periods. This paper also seeks to clarify what criteria should be relevant to the determination of a compliance deadline.

This paper highlights factors that arbitrators may find determinative in 21.3(c) proceedings. With regard to domestic constitutional issues surrounding implementation, most arbitral decisions take the position that the amendment of an act by Parliament or Congress is generally more time-consuming than the amendment of an act by the Executive. As to social and political complexity, this paper concludes that simple contentiousness is not a sufficient consideration under Article 21.3(c) to justify a longer period of time. With regard to economic situations, it agrees with the view that economic harm suffered by foreign exporters should not have an impact on what is the shortest period possible within the legal system of the Member to implement the recommendations and rulings of the DSB. As for the mandate of the arbitrator, this paper concludes that it is up to the implementing Member to determine the proper scope and content of anticipated legislation, and that only after the Member has selected how it will implement the DSB's recommendations and rulings, should an arbitrator consider whether the proposed reasonable period of time is the shortest period possible for the anticipated means of implementation within the legal system of that Member. The proper concern of an arbitrator under Article 21.3(c) is when, not what.